2,509 research outputs found
Dynamics of the Light-Cone Zero Modes: Theta Vacuum of the Massive Schwinger Model
The massive Schwinger model is quantized on the light cone with great care on
the bosonic zero modes by putting the system in a finite (light-cone) spatial
box. The zero mode of survives Dirac's procedure for the constrained
system as a dynamical degree of freedom. After regularization and quantization,
we show that the physical space condition is consistently imposed and relates
the fermion Fock states to the zero mode of the gauge field. The vacuum is
obtained by solving a Schr\"odinger equation in a periodic potential, so that
the theta is understood as the Bloch momentum. We also construct a one-meson
state in the fermion-antifermion sector and obtained the Schr\"odinger equation
for it.Comment: 23 pages, RevTex, no figure
Differential membrane binding of α/ÎČ-peptide foldamers: implications for cellular delivery and mitochondrial targeting
The intrinsic pathway of apoptosis is regulated by the Bcl-2 family of proteins. Inhibition of the anti-apoptotic members represents a strategy to induce apoptotic cell death in cancer cells. We have measured the membrane binding properties of a series of peptides, including modified α/ÎČ-peptides, designed to exhibit enhanced membrane permeability to allow cell entry and improved access for engagement of Bcl-2 family members. The peptide cargo is based on the pro-apoptotic protein Bim, which interacts with all anti-apoptotic proteins to initiate apoptosis. The α/ÎČ-peptides contained cyclic ÎČ-amino acid residues designed to increase their stability and membrane-permeability. Dual polarisation interferometry was used to study the binding of each peptide to two different model membrane systems designed to mimic either the plasma membrane or the outer mitochondrial membrane. The impact of each peptide on the model membrane structure was also investigated, and the results demonstrated that the modified peptides had increased affinity for the mitochondrial membrane and significantly altered the structure of the bilayer. The results also showed that the presence of an RRR motif significantly enhanced the ability of the peptides to bind to and insert into the mitochondrial membrane mimic, and provide insights into the role of selective membrane targeting of peptides
Electromagnetic duality and light-front coordinates
We review the light-front Hamiltonian approach for the Abelian gauge theory
in 3+1 dimensions, and then study electromagnetic duality in this framework.Comment: 18 pages, LaTeX, 2 references and a typo in an eqn. (19) corrected,
minor revisions in response to referee's repor
Bubble Shape Oscillations and the Onset of Sonoluminescence
An air bubble trapped in water by an oscillating acoustic field undergoes
either radial or nonspherical pulsations depending on the strength of the
forcing pressure. Two different instability mechanisms (the Rayleigh--Taylor
instability and parametric instability) cause deviations from sphericity.
Distinguishing these mechanisms allows explanation of many features of recent
experiments on sonoluminescence, and suggests methods for finding
sonoluminescence in different parameter regimes.Comment: Phys. Rev. Lett., in pres
The (1+1)-dimensional Massive sine-Gordon Field Theory and the Gaussian Wave-functional Approach
The ground, one- and two-particle states of the (1+1)-dimensional massive
sine-Gordon field theory are investigated within the framework of the Gaussian
wave-functional approach. We demonstrate that for a certain region of the
model-parameter space, the vacuum of the field system is asymmetrical.
Furthermore, it is shown that two-particle bound state can exist upon the
asymmetric vacuum for a part of the aforementioned region. Besides, for the
bosonic equivalent to the massive Schwinger model, the masses of the one boson
and two-boson bound states agree with the recent second-order results of a
fermion-mass perturbation calculation when the fermion mass is small.Comment: Latex, 11 pages, 8 figures (EPS files
Mesons in the massive Schwinger model on the light-cone
We investigate mesons in the bosonized massive Schwinger model in the
light-front Tamm-Dancoff approximation in the strong coupling region. We
confirm that the three-meson bound state has a few percent fermion six-body
component in the strong coupling region when expressed in terms of fermion
variables, consistent with our previous calculations. We also discuss some
qualitative features of the three-meson bound state based on the information
about the wave function.Comment: 19 pages, RevTex, included 6 figures which are compressed and
uuencode
Zero Mode and Symmetry Breaking on the Light Front
We study the zero mode and the spontaneous symmetry breaking on the light
front (LF). We use the discretized light-cone quantization (DLCQ) of
Maskawa-Yamawaki to treat the zero mode in a clean separation from all other
modes. It is then shown that the Nambu-Goldstone (NG) phase can be realized on
the trivial LF vacuum only when an explicit symmetry-breaking mass of the NG
boson is introduced. The NG-boson zero mode integrated over the LF
must exhibit singular behavior in the symmetric limit
, which implies that current conservation is violated at zero
mode, or equivalently the LF charge is not conserved even in the symmetric
limit. We demonstrate this peculiarity in a concrete model, the linear sigma
model, where the role of zero-mode constraint is clarified. We further compare
our result with the continuum theory. It is shown that in the continuum theory
it is difficult to remove the zero mode which is not a single mode with measure
zero but the accumulating point causing uncontrollable infrared singularity. A
possible way out within the continuum theory is also suggested based on the
`` theory''. We finally discuss another problem of the zero mode in the
continuum theory, i.e., no-go theorem of Nakanishi-Yamawaki on the
non-existence of LF quantum field theory within the framework of Wightman
axioms, which remains to be a challenge for DLCQ, `` theory'' or any other
framework of LF theory.Comment: 60 pages, the final section has been expanded. A few minor
corrections; version to be published in Phys. Rev.
The Role of Zero-Modes in the Canonical Quantization of Heavy-Fermion QED in Light-Cone Coordinates
Four-dimensional heavy-fermion QED is studied in light-cone coordinates with
(anti-)periodic field boundary conditions. We carry out a consistent light-cone
canonical quantization of this model using the Dirac algorithm for a system
with first- and second-class constraints. To examine the role of the zero
modes, we consider the quantization procedure in {the }zero-mode {and the
non-zero-mode} sectors separately. In both sectors we obtain the physical
variables and their canonical commutation relations. The physical Hamiltonian
is constructed via a step-by-step exclusion of the unphysical degrees of
freedom. An example using this Hamiltonian in which the zero modes play a role
is the verification of the correct Coulomb potential between two heavy
fermions.Comment: 22 pages, CWRUTH-93-5 (Latex
Variational Mass Perturbation Theory for Light-Front Bound-State Equations
We investigate the mesonic light-front bound-state equations of the 't Hooft
and Schwinger model in the two-particle, i.e. valence sector, for small fermion
mass. We perform a high precision determination of the mass and light-cone wave
function of the lowest lying meson by combining fermion mass perturbation
theory with a variational approach. All calculations are done entirely in the
fermionic representation without using any bosonization scheme. In a
step-by-step procedure we enlarge the space of variational parameters. For the
first two steps, the results are obtained analytically. Beyond that we use
computer algebraic and numerical methods. We achieve good convergence so that
the calculation of the meson mass squared can be extended to third order in the
fermion mass. Within the numerical treatment we include higher Fock states up
to six particles. Our results are consistent with all previous numerical
investigations, in particular lattice calculations. For the massive Schwinger
model, we find a small discrepancy (less than 2 percent) in comparison with
known bosonization results. Possible resolutions of this discrepancy are
discussed.Comment: some points clarified, representation straightened, to appear in
Phys. Rev. D, 31 pages, Latex, REVTeX, epsfig, 3 postscript figures include
Nonperturbative Light-Front QCD
In this work the determination of low-energy bound states in Quantum
Chromodynamics is recast so that it is linked to a weak-coupling problem. This
allows one to approach the solution with the same techniques which solve
Quantum Electrodynamics: namely, a combination of weak-coupling diagrams and
many-body quantum mechanics. The key to eliminating necessarily nonperturbative
effects is the use of a bare Hamiltonian in which quarks and gluons have
nonzero constituent masses rather than the zero masses of the current picture.
The use of constituent masses cuts off the growth of the running coupling
constant and makes it possible that the running coupling never leaves the
perturbative domain. For stabilization purposes an artificial potential is
added to the Hamiltonian, but with a coefficient that vanishes at the physical
value of the coupling constant. The weak-coupling approach potentially
reconciles the simplicity of the Constituent Quark Model with the complexities
of Quantum Chromodynamics. The penalty for achieving this perturbative picture
is the necessity of formulating the dynamics of QCD in light-front coordinates
and of dealing with the complexities of renormalization which such a
formulation entails. We describe the renormalization process first using a
qualitative phase space cell analysis, and we then set up a precise similarity
renormalization scheme with cutoffs on constituent momenta and exhibit
calculations to second order. We outline further computations that remain to be
carried out. There is an initial nonperturbative but nonrelativistic
calculation of the hadronic masses that determines the artificial potential,
with binding energies required to be fourth order in the coupling as in QED.
Next there is a calculation of the leading radiative corrections to these
masses, which requires our renormalization program. Then the real struggle of
finding the right extensions to perturbation theory to study the
strong-coupling behavior of bound states can begin.Comment: 56 pages (REVTEX), Report OSU-NT-94-28. (figures not included,
available via anaonymous ftp from pacific.mps.ohio-state.edu in subdirectory
pub/infolight/qcd
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